The present invention relates to a superconducting magnet and a magnetic resonance imaging apparatus using the superconducting magnet, and particularly to a super conducting magnet suitable for an open-type MRI apparatus not giving blockfeeling to a person to be inspected and an MRI apparatus using the superconducting magnet.
An example of a conventional superconducting magnet used for an MRI apparatus is disclosed in Japanese Patent Application Laid-Open No. 10-179546. The conventional superconducting magnet described in the patent gazette is constructed in such that a coil container containing the superconducting magnet immerged into cooling medium of liquid helium also serves as a helium tank for storing the liquid helium, and a refrigerator for cooling the liquid helium is directly placed in the coil container (the helium container).
Further, a method, in which a flexible portion such as a bellows is placed between a refrigerator and a cryostat portion placing the refrigerator as an accommodation against vibration of the refrigerator, is disclosed in Japanese Patent Application Laid-Open No. 11-16719. Although this method can certainly insulate the vibration between the cryostat and the cold head of the refrigerator, in order to secure the vibration insulation while the cooling performance is being secured, various kinds of such devices as described the above-described patent are necessary and accordingly the cost is increased.
However, the conventional superconductor for the MRI apparatus has the following problems.
That is, since the refrigerator for cooling the liquid helium is directly placed in the coil container, the vibration of the refrigerator is directly transmitted to the coil container, and the superconducting coil contained in the inside is also vibrated by the vibration to vibrate the generated magnetic flux. Since the vibration of the generated magnetic flux gives a bad influence to the image, no clear image can be obtained.
The present invention is made in order to solve the above problems. An object of the present invention is to provide a superconducting magnet in which the vibration of the magnetic flux generated by the superconducting magnet is suppressed so as to not give bad influence to an image by reducing the vibration transmitted from the refrigerator to the coil container containing the superconducting coil, and to provide an MRI apparatus using the superconducting magnet.
In order to attain the above object, the present invention is characterized by an MRI apparatus comprising a superconducting magnet in which the coolant tank for supplying the coolant to the coil containers for containing the superconducting coils together with the coolant are provided separately from the coil containers, and the refrigerator is placed in the coolant tank, and the coolant tank and the coil containers are connected to each other by coolant circulation passage; a bed capable of mounting a body to be inspected and moving between the coil containers of the superconducting magnets opposite to each other; and a control unit for analyzing a nuclear magnetic resonance signal from the body to be inspected.